Mechanical Weathering

Type of Lesson: Hands-on activity and discussion

Time Needed: 45 minutes, or one full class period

Standards Addressed

Earth and Space Science, Grades K-4: Earth materials are solid rocks and soils, water, and the gases of the atmosphere. The varied materials have different physical and chemical properties, which make them useful in different ways, for example, as building materials, as sources of fuel, or for growing the plants we use as food. Earth materials provide many of the resources that humans use.

Earth and Space Science, Grades K-4: The surface of the earth changes. Some changes are due to slow processes, such as erosion and weathering, and some changes are due to rapid processes, such as landslides, volcanic eruptions, and earthquakes.

Earth and Space Science, Grades 5-8: Some changes in the solid earth can be described as the “rock cycle.” Old rocks at the earth’s surface weather, forming sediments that are buried, then compacted, heated, and often recrystallized into new rock. Eventually, those new rocks may be brought to the surface by the forces that drive plate motions, and the rock cycle continues.

Earth and Space Science, Grades 9-12: Interactions among the solid earth, the oceans, the atmosphere and organisms have resulted in the ongoing evolution of the earth system. We can observe some changes such as earthquakes and volcanic eruptions on a human time scale, but many processes such as mountain building and plate movements take place over hundreds of millions of years.

Physical Science, Grades K-4: Objects have many observable properties, including size, weight, shape, color, temperature, and the ability to react with other substances. Those properties can be measured using tools, such as rulers, balances, and thermometers.

Physical Science, Grades 5-8: A substance has characteristic properties, such as density, a boiling point, and solubility, all of which are independent of the amount of the sample. A mixture of substances often can be separated into the original substances using one or more of the characteristic properties.

Quick Summary of Lesson

This experiment will guide students in comparing the weathering of different materials.

Materials

Procedure

1. Each group of 2-3 students should obtain a weighed rock or mineral sample in a plastic jar. Record the weight of the sample on the worksheet.
2. Fill the jar 1/4 way with water. Screw the lid on tightly.
3.Shake the jar at a steady rate for ten minutes (you may want to share the shaking!).
4. Open the jar and rinse away the loose sediment. Pat the sample dry and get it weighed (by the teacher or assistant). Record this weight on your worksheet and mark it on the jar.
5. Write down some observations about your sample. (Has the size, shape or color changed at all?)
6. Return your sample to the jar. Clean up your work area.
7. Complete the chart on your worksheet and fill in your result on the blackboard. To figure out the "% change" take the "change in weight" and divide it by the "weight before shaking" and multiply it by 100. (For example, if the sample weighed 100 grams before it was shaken and 75 grams after, its change in weight was 100g-75g=25 g. Now 25 grams divided by 100 grams is .25. Multiply that by 100 to get 25%.
8. Be sure and copy the results on the board from other groups!
9. Answer all the questions on the worksheet.

Student Activity Sheet

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Notes to the Teacher

The purpose of the lab is to compare the weathering of different materials. The class will work in groups. Each group will be responsible for performing the procedures for one rock or mineral. The group must then share their results with the rest of the class as well as get other results so that a comparison can be made.

Rocks and minerals undergo physical and chemical weathering. One type of weathering that rocks and minerals undergo is when water dissolves the minerals. Some minerals are more resistant to weathering than others. For instance, quartz is a very resistant mineral.

Surface area also affects weathering; the more surface area exposed, the more weathering that will take place.